"Everyone Knows"

The way to manipulate the majority is not through direct and overt convincing of a point, but to shape the background noise of their life. If the media they consume, stories that they hear, and rumors that are spread generally conform to a certain set of assumptions, those beliefs will gradually become accepted by the average person at least in a fuzzy sense. Keep it up long enough and things that challenge those assumptions will be seen as increasingly ludicrous - even if those challenges are the truth itself.

Specific historical examples: Japan's educational system during the Meiji restoration, which trained millions of youths that Japanese were racially superior to other Asians and Japan's manifest destiny to rule the Pacific; Mao's spread of communism after driving out the GMD from mainland China; and, the Catholic Church in medieval times.

This is why appeals to popularity are invalid arguments. "Everyone knows" is not a basis of fact; in fact, as history shows, what "everyone knows" is frequently wrong. (A corollary is that just because something is widely held doesn't make it wrong by necessity - it only increases the likelihood.) Skepticism should increase the more people seem to assume a fundamental principle without evidence. Demand proof, not popularity.

For example, one reason I like the Bill Nye and Ken Hamm debate on evolution is that Nye was able to make his case without a resort to popularity. He didn't have to say "but everyone knows this." He came in with facts, math, and logical arguments that showed why evolution has earned its place as the dominant theory. Evolution isn't true because a majority of scientists subscribe to it; a majority of scientists accept it because it has the evidence to back it up.

Contrast that positive example with a lot of what passes for arguments these days. "Everyone knows that this viewpoint means you're a nut," "everyone knows that no religion makes you evil," or "everyone knows that government does what's best." Hoyt coined the phrase "Argument by posturing." I think that's a good way to describe the attitude underlying those who use this kind of tactic to marginalize others.